This invention relates to an intake passage for a multi-cylinder engine and more particularly to an improved intake system for multi-cylinder engines.
It has been proposed with multi-cylinder engines to employ an induction system that incorporates a plenum chamber for supplying a charge to the combustion chambers of the engine. The plenum chamber tends to damp out pulsations in the intake charge and avoids a loss of volumetic efficiency. However, it has been found that the provision of a single air intake for the plenum chamber tends to restrict the breathing capacity of the engine at high speeds and, accordingly, can reduce the high speed output of the engine. In order to overcome these difficulties, it has been proposed to employ an intake system that includes a pair of atmospheric air inlets for the plenum chamber. However, it has been found that the use of plural atmospheric inlets for the plenum chamber, even though it may increase the maximum performance of the engine, tends to provide a dip or valley in the mid-range torque curve.
It is, therefore, a principal object of this invention to provide an improved intake system for an internal combustion engine employing a plenum chamber.
It is a further object of this invention to provide an improved intake system for an internal combustion engine wherein the plenum chamber is provided with a plurality of controlled inlets for improving the mid-range torque of the engine.
Because of the compromise in the normal design of the length and cross-sectional area of the intake passages for an internal combustion engine, it has been suggested to improve the engine performance by providing a compound induction system that includes a pair of differently tuned intake passages for serving each combustion chamber. In accordance with such an arrangement, it is also desirable to provide plenum chambers for serving the different length intake passages. Such a system is shown in copending application Ser. No. 634,795, filed July 26, 1984, in the names of Masatoshi Ohmi et al, entitled "Intake Means Of Internal Combustion Engine", and assigned to the assignee of this application. This type of induction system is a substantial improvement over prior art systems but still offers the opportunity for further improvement, particularly in maximum output. For example, there is disclosed in copending application Ser. No. 002,730, filed Jan. 14, 1987, in the names of Iwao Masumoto et al, entitled "Intake System For Multi Cylindered Engine" and assigned to the assignee of this application an arrangement wherein each plenum chamber has plural inputs to increase maximum power output. Such compound systems using plenum chambers and plural air inlets may, in some instances, present some of the disadvantages as aforenoted with respect to valleys in mid-range torque.
It is, therefore, a still further object of this invention to provide an improved induction system for internal combustion engines having compound intake passages.
It is a further object of this invention to provide an improved intake system for a multi-cylinder engine that will improve performance throughout the entire engine load and speed ranges.